Hello everyone! I am part of a university club that has received ~$2,500 in funding to build a wooden trebuchet as part of an engineering project. While we plan to construct later on in the year, we are facing the issue that we must spend $1,000 of the funding or lose it by the end of next week. Additionally, a further $3,500 is in flux, which we will not know if we have been awarded until the new year.
Given these constraints, we are unsure of what materials to buy before the end of next week. We don’t want to buy beams that are too small, as if we receive the additional funding then the size of our trebuchet will increase. However, if we do not receive the funding, we don’t want to be stuck with super large beams we cannot feasibly use.
Does anyone have any blueprints or ideas we could learn from? Our current plan is to get as many 2”x4” beams or 4”x4” beams, as we think those are the most adaptable to different trebuchet sizes. Any help would be appreciated, thank you!
Depends on your material choice and scale. You’ll need a counterweight which can be expensive if you’re not using borrowed free weights. I have used 2x4’s which you can buy and store and cut to scale later. I would also highly recommend 80/20 or some other aluminum extrusion beam. You can get a bunch of lengths of beam now and once you’ve done the design get the hardware you need later.
I see now that you said wood so I guess ignore the 80/20 but still a good product to know about.
So I guess you should guesstimate your scale and buy lumber with maybe a factor of safety of 3. 2 if you have experienced wood workers.
We’re aiming for 40-feet to the axel. Is this feasible? I’m not sure 2x4s would hold up at that scale.
Would you recommend 25-feet instead?
Oh wow that’s gonna be huge. I hope you post updates somewhere. I would not go 2x4’s at that scale. But at 40 ft I wouldn’t recommend wood. Without knowing more about your concept and the scope of the project I would expect other materials to end up cheaper.
YouTube a video of the building of the WarWolf trebuchet replica - which is the scale you are thinking of ( but still not 40’ ) The beams are 12” x12” timbers.
2 x4’s are totally inadequate for a treb of that size. Life long carpenter and treb enthusiast.
As long as it can throw a 90kg projectile over 300m you’re fine
If you need to spend $1k in funding right now, a 4"x12"x40' glulam is about $1k after taxes and delivery.
That would be awesome, do you have a link to that? Would be perfect for the throwing arm
Delivery on engineered wood products are very region based. Start by looking up truss supply companies in your area. They manufacture beams and trusses. Or lumber supply companies, you are looking for building lumber not fencing lumber. Less likely option is big box stores can special order them, but typically don't. They need to be manufactured so don't expect them to have them in stock, but you can get a purchase order going to satisfy your end of the year grant requirements.
Something like this https://www.mccoys.com/shop/p/01410257/3-12x11-78-40-glulam-21e